Isomerization of tertiary alkyl bromides



United States Patent 3,214,480 ISOMERIZATION OF TERTIARY ALKYL BROMIDES William D. Hoffman, Park Forest, Ill., assignor to Sinclair Research, Inc., Wilmington, Del., a corporation of Delaware No Drawing. Filed July 24, 1962, Ser. No. 212,148 4 Claims. (Cl. 260658) The present invention relates to a novel method for obtaining high selective yields of secondary bromides from tertiary bromides. In another embodiment the invention concerns the production of high yields of olefins; particularly terminal isoolefins having a double bond in the 1 position and a tertiary carbon atom in the 3 or higher position.

Since the advent of the Ziegler method for polymerizing terminal olefins, there is a need for a general process for the production of terminal isoolefin feedstocks. Although a typical refinery stream contains most of the various isoolefins such as 3-methyl-butene-1 which might be raw materials for these polymers, the concentrations are generally quite low. One possible method of increasing the concentration of the desirable raw materials is isomerization of other isomers to the desired one. In these processes, however, the conversion of feed to the desired products is limited by the thermodynamic equilibrium concentration of the olefin at the temperature of the reaction.

It has been discovered that the thermal pyrolysis of secondary bromides effects terminal olefin yields 4 to 6 times that obtained by the ordinary isomerization processes. These secondary bromides, however, are not readily available, and known processes for their production have heretofore either been too expensive and/or incapable of producing selective yields.

It has now been found that high selective yields of secondary bromides can be obtained by contacting a tertiary bromide under isomerization conditions with a catalyst consisting essentially of a metal selected from the group consisting of cobalt, nickel, platinum and palladium on charcoal as a support. The isomerization conditions can include a temperature of about 0 to 850 F., preferably about 200 to 500 F., a pressure of about 1 atmosphere or less to about 45 or more atmospheres, preferably about 1 to 30 atmospheres, and a weight hourly space velocity (WHSV) of about 0.1 to 20, preferably about 1 to 10.

The tertiary bromide feed of the present invention can be represented by the structural formula:

wherein R is a lower alkyl group say of l to 8 carbon atoms, and n equals 1 to 10, preferably 1 to 3.

The metal component of the isomerization catalyst of the present invention is present on the charcoal support in small catalytic amounts. Any known method of the art can be employed to effect deposition of the metal as, for instance, by impregnation with an aqueous solution of a water-soluble salt of the metal, precipitation of the metal component on the support, direct mixing of the metals per se or salts thereof with the charcoal support, etc. Combinations of the catalytic metal or salts thereof can be employed if desired. In general, the catalytic metal will constitute about 0.1 to 10 percent by weight of the catalyst, preferably about 1 to 10 percent by weight in the case of nickel and cobalt and about 0.1 to 2 percent by weight with respect to platinum and palladium.

3,214,480 Patented Oct. 26, 1965 Isornerization of the tertiary bromide feed in accordance with the above-described method will produce a secondary bromide in high selective yields without cracking or skeletal isomerization to other secondary bromides of similar carbon content. If olefin production is desired, the secondary bromide can then be pyrolyzed at elevated temperatures, for instance, about 600 to 1050 F., preferably about 700 to 900 F. with or without a catalyst. Advantageously the pyrolysis is conducted in the presence of a contact material that is essentially non-catalytic and essentially free of acidic and basic materials. Suitable contact materials are, for example, pyrex beads, coke, etc. When a contact material is employed a LHSV (liquid hourly space velocity) of about 0.1 to 30, preferably about 0.5 to 10 is generally used. The pyrolysis can be conducted at atmospheric pressure but subatmospheric or superatmospheric pressures are usable as well.

To obtain terminal olefins from the pyrolysis of the secondary bromide, the secondary bromide must have the bromine atom located in the 2 position and whether or not the secondary bromide is of this type depends on the tertiary bromide feed selected for the isomerization. isomerization by the method of the present invention of a tertiary bromide feed having the structural formula:

where R is a lower alkyl radical of say 1 to 8 carbon atoms provides a secondary bromide which on pyrolysis directly produces terminal olefins. Terminal olefins, however, can easily be obtained from secondary bromides which do not contain the halide in the 2 position by HBr addition to the non-terminal olefins obtained by pyrolysis of these secondary halides and again pyrolyzing the resulting secondary bromide to olefin. Should a single bromination and subsequent pyrolysis be insufficient to produce the terminal olefin, the bromination-pyrolysis sequence can be repeated the number of times necessary to obtain the terminal olefins, that is, until such time as the HBr addition provides a secondary bromide having the halide in the 2 position, pyrolysis of which gives the terminal olefin. The HBr addition can be conducted at about room temperature up to 200 F. and with if desired a catalyst favoring HBr addition. Generally about 0.1 to 5 moles of HBr per mole of olefin, preferably about 1 to 2 moles of HBr per mole of olefin are employed.

The following examples are included to further illustrate the present invention.

EXAMPLE I A five percent nickel on charcoal catalyst was charged to a 1-inch glass reactor. A syringe pump was filled with 32 ml. of 2-bromo-2-methyl pentane and this tertiary bromide was passed over the catalyst at 400 F. and a weight hourly space velocity of 1. After the reaction terminated, the resulting product was analyzed by gas chromatography. The results were as follows:

Wt. percent Cis 4-methyl-2-pentene 1.00 Trans 4-methyl-2-pentene 4.90 3-bromo-2-methylpentane 33.15 2-broIno-2methylpentane 59.27

The data illustrate that the tertiary bromide isomerization process of the present invention is capable of providing high selective yields of secondary bromides without skeletal isomerization or cracking. Higher conversions yet are obtainable with the use of more severe conditions.

3 EXAMPLES 114v Results similar to those found in Example I can be obtained by isomerizing 2-bromo-2-methyl-pentane under the conditions of Example I with the following catalysts:

II. 0.5% Pt on charcoal III. Co on charcoal IV. 0.5% Pd on charcoal EXAMPLE V 3-bromo-2-methylpentane was pyrolyzed under the conditions shown in Table I below. The pyrolysis was conducted in a glass reactor packed with Pyrex beads. A syringe pump was used for feeding the 3-bromo-2-methylpentane. The reaction product was quenched directly from the reactor with water and analyzed by gas chromatography. The results are also shown in Table I.

Table I PYROLYSIS OF 3-BROMO-2-METHYLPENTANE Run-" 1200-3 1200-4 Temperature, F. 750 750 LHSV, ce./cc 6 1. 8 Conversion, percen 52 37 Products (Mole percent):

Cis 4-methyl-2-pentene 5. 5 7. 2 Trans 4-methyl-2-peutene 31. 6 32. 2 2-methyl-2-pentene 1 62. 8 G0. 8

1 Recovered as the bromide 3-bromo-2-n1ethylpcntane.

EXAMPLE VI 3-bromo-2-methylbutane is made from 2-bromo-2- methylbutane by use of the catalysts and conditions of Examples I through IV. Pyrolysis of 3-bromo-2-methyl butane was conducted at 800 F, and 24.8 LHSV to give 49.6 mole percent conversion and 29.9 mole percent 3- methyl-l-butene per mole of 3-bromo-2-mcthylbutane converted and at 900 F. and 24.8 LHSV the conversion was 83.6% to provide 18.6 mole percent 3-methyl-1-butene for each mole of 3-bromo-2-methylbutane converted It is claimed:

1. A method for the production of a secondary bromide which comprises contacting a tertiary bromide feed having the structural formula:

wherein R is a lower alkyl group and n is 1 to 10, under isomerization conditions including a temperature of about '0 to 850 F., and a pressure of up to about atmos- References Cited by the Examiner UNITED STATES PATENTS 1,993,719 3/35 Nutting et al. 260658 2,315,871 4/43 Oberfell et al. 260658 2,467,965 4/49 Chenicek 260658 LEON ZITVER, Primary Examiner. 

1. A METHOD FOR THE PRODUCTION OF A SECONDARY BROMIDE WHICH COMPRISES CONTACTING A TERTIARY BROMIDE FEED HAVING THE STRUCTURAL FORMULA: 